High temperature performance of foamed fly ash geopolymers

Abstract

Nowadays, the environmental sustainability becomes a big issues for an industry when they are going to produce the waste material such as ash and dust. These materials will cause various effects to the environment such as acid rain when it is left to accumulate in the air. To prevent this things from happening, the fly ashes from the coal and wool factory were brought together to produce new coalition called geopolymer paste. Geo in the phrase refers to the ashes while the polymer is referring to the mixture of silicate and alkaline solutions of high concentration. It is a simple method of mixing the liquid part of NaOH (12M concentrations) and Na2SiO3 with fly ash, then the mixture is mix with foaming agent (hydrogen peroxide) to produce paste. The paste is cured under room temperature for 1 day. Next, the paste was heated in a furnace at different temperatures, which were 200oC, 400oC, 600oC, and 800oC. The samples were tested and characterized on their bulk density, compressive strength, microstructure, functional group and thermal properties. The result showed that the bulk density of foamed geopolymers is lightweight (~1400 kg/m3). With the exposure to high temperature, the bulk density of geopolymers has no much change. However, the compressive strength decreased when heated up to 400°C and then increased beyond 400°C. From microstructural analysis, the fly ash geopolymers showed the formation of geopolymer matrix with some unreacted particles. Cracks were formed in the samples. FTIR analysis showed the shift of wavenumber after the exposure of high temperature. In samples heated at 800°C, zeolite band was observed. On the other hand, TGA analysis showed that main weight loss occurred at temperature below 100°C. It is believed that the understanding on the properties of fly ash geopolymers helps in the enhancement of properties of geopolymers in future study.